docs: add docs folder (architecture, developer, usage); update README; wire probe TTL cache + concurrency notes into docs

docs/README.md

@@ -0,0 +1,18 @@
+# Cloudlysis Documentation
+
+## Sections
+- Architecture
+  - docs/architecture/overview.md
+  - docs/architecture/transport.md
+- Developer
+  - docs/developer/setup.md
+  - docs/developer/testing.md
+- Usage
+  - docs/usage/quickstart.md
+  - docs/usage/api.md
+  - docs/usage/nats.md
+
+## Conventions
+- HTTP edge remains JSON over REST via Gateway.
+- Internal RPC uses gRPC between Gateway and nodes (Aggregate, Projection, Runner).
+- Async backbone uses NATS JetStream and KV with standardized subjects, headers, and stream/consumer policies.